Process and converter for refining liquid metals

ABSTRACT

An improvement in the refining of molten metals in a convertor by means of oxygen introduced into the metal through tuyeres which include two concentric pipes, oxygen being passed into the melt through the central pipe and a protective fluid being passed into the melt as a sheath or screen around the oxygen, through the clearance space between the two pipes. In the present invention two or more tuyeres, disposed horizontally and each passing through the convertor sidewall permit refining to be accomplished without any slopping or splashing of the melt and with only minor wear of the convertor lining.

United States Patent [1 Kniippel et al.

[451 Nov. 18, 1975 PROCESS AND CONVERTER FOR REFINING LIQUID METALS [75] Inventors: Helmut Kniippel; Karl Brotzmann;

I-Ians Georg Fassbinder, all of Sulzbach-Rosenberg, Germany [73] Assignee: Eisenwerk-G esellschaft Maximilianshutte mbH, Sulzbach-Rosenberg, Germany 22] Filed: Oct. 2, 1973 21 App1.No.:402,695

30 Foreign Application Priority Data Oct. 3, 1972 Canada 153166 [52] US. Cl 75/60; 75/59 [51] Int. Cl. C21c 5/34 [58] Field of Search 75/59, 60

[56] References Cited UNITED STATES PATENTS 5/1961 Johnson 75/60 3,015,554 1/1962 Rummel 75/60 3,791,813 2/1974 Ramachandran 75/60 3,802,685 4/1974 Brisse 75/60 FOREIGN PATENTS OR APPLICATIONS 1,450,718 7/1966 France 75/60 Primary Examiner-P. D. Rosenberg Attorney, Agent, or Firm.l .awrence I. Field 57] ABSTRACT An improvement in the refining of molten metals in a convertor by means of oxygen introduced into the metal through tuyeres which include two concentric pipes, oxygen being passed intothe melt through the central pipe and a protective fluid being passed into the melt as a sheath or screen around the oxygen, through the clearance space between the two pipes. In the present invention two or more tuyeres, disposed horizontally and each passing through the convertor sidewall permit refining to be accomplished without any slopping or splashing of the melt and with only minor wear of the convertor lining.

6 Claims, 2 Drawing Figures Sheet 1 of 2 US. Patent NQv. 18, 1975 US. Patent Nov. 18, 1975 Sheet 2 of2 3,920,448

PROCESS AND CONVERTER FOR REFINING LIQUID METALS The invention relates to a process for refining molten metals in vessels lined with refractory materials, by the use of oxygen surrounded by gaseous or liquid hydrocarbons and introduced through the side masonry of the vessel and underneath the surface of the molten metal, and to the convertor wherein such a process is achieved. I I

A process wherein oxygen surrounded by a protective veil of hydrocarbon is introduced below the bath surface for refining metal melts is described in US. Pat. No. 3,706,549 issued Dec. 19, 1972. This process makes use of tuyeres mounted in various groupings in the convertor bottom for refining pig iron into steel. The present invention is an improvement over the process of said patent, the disclosure of which is intended to be incorporated herein as representing the prior art.

Although the process is presently enjoying commercial success, various difficulties have been experienced from time to time in carrying out the process. In the use of such a convertor it is found that frequently the blowing will be quite agitated and that further there may be ejection of slag and steel jets the moment the bath level reaches the area of the tuyeres when tilting the convertor, e.g. for purposes of making additions or for taking samples. 9

The present invention is directed to retaining the advantages of refining by means of oxygen tuyeres mounted below the bath surface while further developing the process so as to obtain quiet blowing, minor wear of the refractorylining and high filling efficiency and to the means by which this is achieved.

Surprisingly, it was found that the desired improvements were obtained by mounting at least two tuyeres laterally in such manner that the kinetic energies of the media blown in or otherwise introduced through the tuyeres are partly eliminated. Preferably the tuyeres will be horizontal when the vessel is in the refining position.

The preferred arrangement of tuyeres comprises one or more pairs oppositely located in the sidewalls of the refining vessel and provides special advantages in controlling the bath motion. If the tuyeres are directly and oppositely aligned with each other, the kinetic energy of the fluids discharged by the tuyeres will be nearly entirely eliminated and a horizontal rotational motion of the melt will be avoided. If the tuyeres are mountedat an angle with respect to the straight line connecting them, the metal bath may besubjected to a rotational impulse. This leads to a horizontal bath circulation in the refining vessel. In this kind of arrangement, the tuyeres may deviate in direction no more than 20 from the straight line connecting them. If this value is ex-' ceeded, an undesirably large bath rotation will occur, which causes rapid wear of the side-wall masonry of the convertor vessel lining.

By properly selecting the angle at which the tuyeres will be set with respect to their straight line connection, and taking into account the size of the convertor and its filling level, bath motion may be controlled. A moderate bath rotation is set for the refining process of the invention. This rotation enhances quiet blowing and preventseejection -a d spattering during refining. Furthermore, this rotation causes an equalizationof concentration of constituents in the melt, which is favorable to the refining.

Especially for symmetrical convertors with shapes such as that .shown in FIGS. 8 and 9 of U.S. Pat. 3,706,549 there are particular advantages in the pairwise arrangement of'the refining tuyeres provided they always be built-inbelow the convertor trunnions or pivots. The height of the tuyere installation should be approximately 20-60 cm above bottom level for a newly prepared convertor. In addition to the controlled bath motion, there is also the advantage of high convertor filling efficiency for such built-in height, because the tuyeres will still emerge from and clear the bath even for great loads when the convertor is in the horizontal convertor position, that is, during discharge and sampling. This permits utilization of relatively small convertor volume of the order of magnitude of 0.6 m /ton of steel, whereas for otherwise equal conditions and when the refining gas tuyeres are located in the convertor bottom, a convertor volume exceeding 0.8 m lton of steel is usually required.

' The oppositely arrayed tuyeres provide special adyantages as regards lining life, since this arrangement prevents the media blown-in with high kinetic energies or high speeds of flow from impinging on the convertor wall opposite the tuyere. When making use of a single tuyere, the convertor wall located opposite to the tuyere is subjected to rapid wear on account of the unbraked kinetic energy of the refining gas jet.

A further variation of the invention consists in mounting a group of tuyeres in the region below the convertor pivots or trunnions in convertors tiltable to both sides and used for refining pig iron into steel. In this variation, the tuyere array of opposite wall locations in a circular or nearly circular refining vessel no longer consists of individual or single tuyeres, but rather of groups of tuyeres, each group contains a maximum of ten tuyeres and preferably from two to five tuyeres.

The invention will be more clearly understood from the description which follows taken in conjunction with the drawings in which:

FIG. 1 is a horizontal view partly in section of a symmetrical convertor, taken in the plane of the tuyeres; and

FIG. 2 is a horizontal section of a bottom blown convertor modified for the practice of the present invention.

The convertor shown in FIG. 1 consists of a steel plate casing 1 lined with a solid refractory masonry 2. Tuyeres 3 are mounted below trunnions 4 shown in dashed lines and located in a plane above the tuyeres.

' Each of the tuyeres consists of two concentricpipes 5 ,ant ceramic layer 6. Oxygen alone or oxygen loaded with lime dust is fed from a supply' line 7 through inner pipe 5. Pipe 5 is concentrically surrounded by an ordinary steel outer pipe 8. A protective medium consisting of gaseous or liquid hydrocarbons is introduced through the annular slit 9. between pipes 5 and 8 into the convertor. The angle 11 subtended by line 12 dire ctly connecting the mouths of 'the tuyeres 3 of each tuyere pair and the longitudinal tuyere axis 13 indicates the built-in orientation of each of the pair of tuyeres.

' Line IZ niay be a plane through the longitudinal axis of the'convertorvessel and containing the trunnion axis.

Example 1 A convertor with a capacity of 200 tons-of crude steel was used. The inside diameter of the convertor was 5.5 m, the height was 5.8 m, and the capacity of the convertor was 124 m The specific convertor volume obtained from these values is 0.62 m lton of crude steel. A pair of oppositely located tuyeres was built into the lower side wall of the convertor in a plane 60 cm above the convertor bottom. Immediately underneath the trunnions, the two tuyeres were in horizontal position and made an angle of with respect to the convertor diameter. The convertor masonry may be made thicker by some cm in the region of the tuyere orifices, to prolong the life of a campaign.

The tuyeres each consisted of two concentric pipes, the inner one being coated with a wear-resistant ceramic so as to protect it against abrasion when limedust loaded oxygen is being passed through. The internal diameter of the pipe introducing the refining gas was 90 mm. The width of the annular slit between the inner and outer pipes was 2 mm. The oxygen was passed through the inner pipe at the rate of 50,000 N m /hr (cubic meters measured at standard pressure and temperature) and at a pressure of 10 atm. gauge. On the average, the oxygen was loaded with about 1.2 kg/m of oxygen of lime dust during the refining time. Natural gas at the rate of 2,500 N m /hr and at a pressure of 8 atm. gauge was introduced into the vessel through the annular slit as the protective medium. The natural gas consisted of about 90% methane, 8% other hydrocarbons and 2% nitrogen. The convertor was loaded with 150 tons of pig iron of the following composition:

4.2 7: carbon 0.9 7: silicon 0.6 70 manganese 0.15 7: phosphorus 0.05 7: Sulfur balance iron and 70 tons of scrap was charged. The charge was refined to steel within 12 minutes, the steel being of the following composition:

0.03 77: carbon 0.15 7: manganese 0.008 7: phosphorus 0.022 7c sulfur 0.0025 nitrogen balance iron Observation of the refining of a large number of melts has shown that the metal melt will rotate about the convertor longitudinal axis when the tuyeres are located as described above (10 inclination). Local wear at the lower side wall, such as had been observed for larger angles of inclination of the tuyeres, were not observed in the arrangement mentioned. Neither spattering nor ejection were observed during refining. On the whole, blowing was quiet.

Example 2 A convertor for refining an 80-ton melt was used. The convertor hada capacity of 50 m The inside dimensions were 4 meters for the diameter and 5 meters for the height. A pair of oppositely located tuyeres was mounted horizontally underneath the tilting axis of the convertor and 50 cm above the bottom. The tuyeres were mounted so as to subtend only a small angle of about 5 with respect to their direct connecting line. Each tuyere consisted of an inner copper pipe 5, having an internal diameter of 56 mm and of a concentric outer pipe 8 made of steel. Between the pipes an annular slit of 0.75 mm existed permitting flow of light fuel oil which served as protective medium; about 360 liters/hr of the light oil passed through the slit, the pressure being about 3 atm. gauge, and 10,000 N m lhr of oxygen at a gauge pressure of 10 atm. was passed through the inner pipe 5 of each tuyere. A pig iron of the following composition was refined:

3 .6 7: carbon 1 .6 7c phosphorus 0.3 7: silicon 0.3 7: manganese 0.04 7c sulfur balance essentially iron.

55 tons of this pig iron together with 25 tons of scrap and 8 tons of lump lime were loaded into the convertor. After about 11 minutes, crude steel of the following composition was obtained:

0.02 7c carbon 0 .025 phosphorus 0.08 manganese 0.025 7: sulfur balance essentially iron In this example too there was very quiet blowing, free from ejections, compared to an ordinary bottom blown convertor.

Example 3 A rebuilt convertor for refining steel by the upward oxygen blowing process was employed. Two oppositely located tuyeres were built into the refractory lining below the trunnions. They are essentially mounted horizontally. FIG. 2 shows a section through the convertor, taken about 50 cm above the bottom. It was found to be of particular advantage to modify the refractory as shown in the drawing as compared to the refractory provided in a conventional convertor with upward blowing. The refractory masonry, which is about cm thick in the conventional convertors with upward blowing, is provided in this thickness only in the region of the tuyeres. It was diminished elsewhere in the manner shown in the drawing so that an approximately oval cross section is obtained. This modification is practical because the life of the lining is appreciably longer in a convertor with a pair of tuyeres mounted below the bath surface and in the side wall than is the case for convertors wherein oxygen is being blown up through the bath. The thickening for this region also may be eliminated approximately 1 meter above the tuyeres, so that in that area there will again exist a circular cross section with an average wall thickness of the refractory lining of about 50-60 cm. This modification of the refractory lining permits an appreciable increase in the weight of the melt which can be present in the convertor, in view of the reduction of the weight of the convertor proper. Furthermore, this configuration of the refractory lining permits the specific convertor volume to be reduced to about 0.55 m lton of steel, when the convertor is newly constructed. Such considerations provide considerable economic advantages regarding lar horizontal cross section wherein a stream of oxygen gas surrounded by a separate stream of fluid hydrocarbons is introduced into the molten metal underneath the bath surface, through at least one tuyere which includes an inner pipe for the oxygen and an outer pipe concentric with the inner pipe, the space between said pipes being for the introduction of said fluid hydrocarbons, the improvement which comprises:

introducing the oxygen and hydrocarbons through at least one pair of opposed tuyeres in order to achieve the desired control of bath motion, said tu- 4 6 yeres being located in the lateral side wall of said refining vessel and being arranged so that the angle between each tuyere and a diameter connecting the discharge ends of each pair of tuyeres does not exceed 20.

2. The process of claim 1 wherein the metal to be refined is pig iron.

3. The process of claim 1 wherein there is only one single pair of refining tuyeres and they are disposed horizontally when the convertor is in its refining position. I

4.'The process of claim 1 wherein a pair of tuyeres is mounted below the trunnions of said convertor.

5. The process of claim 1 wherein each pair consists of several tuyeres arrayed in groups located in the convertor in the wall region below the trunnions.

6. The process of claim 1 wherein said tuyeres in the refining vessel are mounted approximately 20-60 cm above the bottom level of the vessel. 

1. IN A PROCESS FOR REFINING METAL IN A REFRACTORY, MASIONARY LINED REFINING VESSEL WITH A NEARLY CIRCULAR HORIZONTAL CROSS SECTION WHEREIN A STREAM OF OXYGEN GAS SURROUNDED BY A SEPARATE STREAM OF FLUID HYDROCARBONS IS INTRODUCED INTO THE MOLTEN METAL UNDERNEATH THE BATH SURFACE, THROUGH AT LEAST ONE TUYERE WHICH INCLUDES AN INNER PIPE FOR THE OXYGEN AND AN OUTER PIPE WHICH INCLUDES AN INNER PIPE FOR THE OXYGEN AND AN SAID PIPES BEING FOR THE INTRODUCTION OF SAID FLUID HYDROCARBONS, THE IMPROVEMENT WHICH COMPRISES: INTRODUCING THE OXYGEN AND HYDROCARBONS THROUGH AT LEAST ONE PAIR OF OPPOSED TUYERES IN ORDER TO ACHIEVE THE DESIRED CONTROL OF BATH MOTION, SAID TUYERES BEING LOCATED IN THE LATERAL SIDE WALL OF SAID REFINING VESSEL AND BEING ARRANGED SO THAT THE ANGLE BETWEEN EACH TUYERE AND A DIAMETER CONNECTING THE DISCHARGE ENDS OF EACH PAIR OF TUYERES DOES NOT EXCEED 20*.
 2. The process of claim 1 wherein the metal to be refined is pig iron.
 3. The process of claim 1 wherein there is only one single pair of refining tuyeres and they are disposed horizontally when the convertor is in its refining position.
 4. The process of claim 1 wherein a pair of tuyeres is mounted below the trunnions of said convertor.
 5. The process of claim 1 wherein each pair consists of several tuyeres arrayed in groups locateD in the convertor in the wall region below the trunnions.
 6. The process of claim 1 wherein said tuyeres in the refining vessel are mounted approximately 20-60 cm above the bottom level of the vessel. 